1. Field of the Invention
The invention relates to an apparatus for applying liquid of a pasty application medium to a moving web, and more particularly a curtain applicator unit, which discharges the application medium onto the web as a curtain or veil.
2. Description of the Related Art
An apparatus for applying liquid of a pasty application medium is disclosed, for example, by WO 98/48113 which is incorporated by reference. Wherein, the excess application medium applied to the edge strips of the web is sucked away from these edge strips. According to an alternative design variant, aperture-stop elements are provided which catch the application medium in the area of the edge strips and in this way do not permit the edge strips to be wetted with application medium. The desire for a reduction in the coverage of the edge strips with application medium is rooted in the desire to eliminate contamination on supporting elements, such as supporting rolls and deflection elements such as deflection rolls which come into contact with the web. The apparatuses which are necessary to clean these elements not only need installation space but also increase the cost of construction and complicate the operating sequence of the overall plant.
The same drawbacks also exist in the systems disclosed by WO 98/47630 and WO 99/09253 each of which are incorporated herein by reference. Wherein adjustable elements, for catching the application medium are provided, just above the web in the transverse direction, in the area of the edge strips of the web.
The invention comprises, in one form thereof, an apparatus which prevents complete coverage of at least one of the edge strips of the web over a predetermined width by deflecting the at least one edge strip out of the plane of the web in the area of the curtain applicator unit. The invention is based on the finding that the deflection of the edge strip out of the plane of the web is sufficient to determine the level of coverage or the coverage transverse profile of the edge strip or to completely avoid the coverage of the edge strip. Therefore, according to the invention, it is possible to dispense completely with aperture-stop elements, that are susceptible to contamination, which are used in the prior art discussed above. As will be explained in more detail below, the deflection device can be arranged in such a way that it is not exposed to risk of contamination from the curtain of application medium or the application medium spray.
In order to achieve the desired level of coverage or the desired coverage transverse profile of the edge strip, the deflection device influences the magnitude and the shape of the deflection of the edge strip.
If residual coverage of the edge strip is permitted (preferably decreasing toward the marginal edge of the web) this can be achieved by the deflection device deflecting the edge strip in such a way that it is deflected through an acute angle in the area of the curtain of application medium. Without taking into account the transverse distribution effects of the application medium, as it is applied to the web, and without taking into account the course of the web in the transition region between the edge strip and the useful strip of the web, the level of coverage in the area of the edge strip, as compared with the application in the area of the useful strip, is reduced by a factor corresponding to the cosine of the acute angle.
If the edge strip is to remain completely uncovered, then the deflection device deflects the edge strip through an obtuse angle in the area of the curtain of application medium. In this configuration the edge strip is xe2x80x9cfolded inxe2x80x9d under the useful strip of the web, such that the useful strip acts as an xe2x80x9caperture-stop elementxe2x80x9d thereby preventing the coverage of the edge strip. However, the coverage of this xe2x80x9caperture-stop elementxe2x80x9d with application medium, is a desired coating with application medium.
According to an embodiment of the invention, the deflection device deflects the edge strip mechanically.
The deflection device includes at least one deflection rod, which acts on the edge strip side facing away from the deflection direction. The deflection rod is arranged to be pivotable about an axis running substantially parallel to the running direction of the web. The deflection rod may be fixed at specific pivoting intervals or be continuously pivotable into desired positions, thereby setting the level of deflection of the edge strip.
To deflect the edge strip gradually, and increasingly, out of the plane of the web, in the running direction of the web, a plurality of deflection rods are provided. The deflection rods are arranged following one another in the running direction of the web.
According to another embodiment of the invention, the deflection device includes at least one deflection strip. The deflection strip acts on the edge strip side facing away from the deflection direction and deflects the edge strip increasingly out of the plane of the web in the running direction of the web. Such a deflection strip is suitable for influencing the shape of the deflection of the edge strip.
Since the at least one deflection rod or the at least one deflection strip is in sliding contact with the web, it is formed from a wear-resistant material.
The at least one deflection rod or the at least one deflection strip may be detachably fitted, to a holder.
In order to avoid contamination of the deflection rod or the deflection strip with application medium the at least one deflection rod or the at least one deflection strip, as viewed in the running direction of the web, is arranged upstream of the position of the curtain applicator unit. The deflection rod or deflection strip is located between about 1 cm and about 20 cm upstream of the position of curtain applicator unit.
According to another embodiment of the invention, the deflection device deflects the edge strip by influencing the air pressure prevailing in the area of the edge strip.
The deflection device includes at least one blowing device whose blowing nozzle is aimed at the edge strip. To stabilize the transition region between the edge strip and the remainder of the web, a blowing nozzle, on the side of the web facing the deflection device, is aimed at the transition region.
As an alternative to the use of blowing devices for deflecting the edge strip and/or for stabilizing the transition region between the edge strip and the remainder of the web, suction devices can be used.
According to another embodiment of the invention, the deflection device can comprise a web moisture influencing device, which deliberately moistens and/or dries the web in predetermined areas of the web. This web moisture influencing device can advantageously act on the transition region between the edge strip and the remainder of the web. For example, the web can be moistened deliberately on its surface facing away from the deflection direction, causing it to swell up locally. Additionally or alternatively, it can be deliberately dried on the surface of the web facing in the deflection direction, causing it to contract. The deliberate moistening and/or drying causes the web to deform resulting in the desired deflection.
In order to ensure the desired shape and the desired level of deflection of the edge strip, for each of the alternative embodiments discussed above, the relative position of the deflection device is adjustable with respect to the web. This allows optimization of the relative position of the deflection device during operation. Furthermore, the deflection device can also be pivoted from the area of the web, for example to facilitate the threading of the web.
To be able to ensure the controlled return of the edge strip into the plane of the web, a deflection or return device can also be provided downstream of the curtain applicator unit in the running direction of the web. This return device can in principle be constructed in the same way as one of the embodiments of the deflection device described above, with the difference being that it does not deflect the edge strip out of the plane of the web, rather it guides it back into the plane of the web.